I assume most of these can be done by tweaking the properties of already existing assets:
Traps and elements to build large traps out of such as:
Wood-bags: look and behave like sandbags except hey are filled with wood-chips and a little something making them really flammable.
Boom-bags: bags filled with crude plastic explosives, as flammable as wood-bags with an added explosiveness
Tar-floor: a wooden floor covered with tar (looks like rough stone floor), highly flammable
Remote Power-doors: open them to lure them in, close them to keep them there
Dumb-bomb: buried explosive or incendiary charge, set off remotely (if connected to grid?) or by fire/explosions
Snare: crafing/other skill used on empty square to place hidden (no art) snare that has a chance to immobilize small animals (and perhaps slow humans/ large animals) disappears after effect is applied, does not differentiate friend and foe, so careless colonists can be affected too, but since no damage is done, it should not present a problem.
Battery safety override: make a battery explode on purpose
Battery forced overload: force a battery to 150% charge for a more memorable blast
Electrified floor: metal/carpet floor tile that uses large amounts of power to damage over time with chance to stun (opens possibility to capture mechanoids for reprogramming but that might be more expensive.. although the stunned mechanoid could just remain offline while a colonist uses the research skill for reprogramming via the same mechanism the social skill is used for recruitment, or the same mechanism used for research, with the amount of tasks a mechanoid can be reprogrammed to do depending on research done in mechanoid reprogramming... but again this may not be the cheapest idea)
Short walls:
Log wall-> mushroom rack - grows mushrooms in the dark, limited lifespan (mushrooms could be a vegetarian alternative to meat in lavish meals)
Wood wall-> cheap weak fence - to keep animals out of crops.
Metal wall-> conveyor belt (this one might not be cheap
... )
Stone wall-> battlement (placeholder name) basically a low wall for shoting over with crenelations for extra cover, a kind of upgraded sandbag
Hollow wall-> wall that colonists can enter and wait in to ambush assailants at close range
Other:
Stinkweed, thorn bush- invasive plants for making besiegers less comfortable while sitting outside the colony (by lowering mood), at the cost of being invasive weeds.
Fruit tree: a tree that gives fruit, basically a combination of the tree model and the berry bush code (i think...)
Meat tree: researchable tree that grows meatfruit
